1. Field of the Invention
The present invention relates to a method and apparatus for diagnosing a fault in a piece of machinery or equipment due to frictional wear, which generates vibrations at a high frequency, as a result of a failure in a rotating, metallic machine element, such as bearings and gears and a lubricant, or as a result of belt slippage in the rotating machine.
2. Description of the Prior Art
A sudden shutdown of production machinery or equipment can be a primary factor in a major accident, and/or it can bring about an extremely large economic loss. At a production site, preventive maintenance is practiced to prevent such a sudden shutdown. As preventive maintenance for avoiding a fault, there is a method called xe2x80x9ccondition-based maintenancexe2x80x9d that grasps the condition of the machinery or equipment by measuring sounds or vibrations being generated by the machinery or equipment in operation. Here, a conventional type of condition-based maintenance will be described, taking vibration measurement as an example.
When measuring vibrations in machinery or equipment to diagnose the existence of a fault, a decision is made as to whether or not the amplitude of the measured vibration exceeds a reference value. Normally, two kinds of reference values are provided for such a decision. If the measured vibration amplitude exceeds the smaller of the reference values, this is considered to be in the domain of caution, wherein operation can be continued, provided that monitoring is frequently performed. On the other hand, if the measured vibration amplitude exceeds the larger of the reference values, this is considered to be in the domain of danger, wherein the operation must be immediately shut down for the machinery or equipment to be repaired.
When the condition of the machinery or equipment reaches the domain of caution, the time when the condition will reach the domain of danger is first estimated from a chart indicating a past tendency of changes from a normal state into the domain of caution. Then, production planning and maintenance planning with the highest economic efficiency are made to carry out the necessary repair.
There are various kinds of machinery or equipment for use in production in a company for which the specifications such as the number of revolutions, electric power consumption, and load vary with the purpose of use. There are also many machines of different shapes and sizes of which the amplitude of vibrations is large or small.
The reference value for decision in diagnosing the existence of a fault is peculiar to each of these pieces of machinery and equipment and is determined by accumulating a quantity of case sample data under fault conditions as well as under normal conditions.
An optimum reference value for decision is therefore needed to show the effect of the condition-based maintenance.
However, there are many companies which cannot determine a reference value for a decision to adopt condition-based maintenance on the grounds that the case sample data during a fault cannot be obtained because the machinery or equipment rarely breaks down. It therefore requires a great deal of labor to determine the reference value for a decision because there are many kinds of machinery or equipment to be diagnosed, and there are no maintenance technicians with much diagnostic knowledge, and the like.
Further, though condition-based maintenance is an economically superior method of maintenance because it can lower the maintenance cost, there are still many companies which cannot determine the reference value for a decision to adopt the condition-based maintenance because the optimum reference value for such a decision is needed to utilize condition-based maintenance as described above.
It is therefore an object of the present invention to solve these problems found in the prior art and to provide a method and apparatus for diagnosing a fault without taking specifications of machinery such as the number of revolutions, electric power consumption, load, and the scale of construction into account.
According to a first aspect of the present invention, a fault diagnosis method is provided, which comprises the steps of detecting vibration waveforms being generated by machinery or equipment, obtaining the ratio (xcex21) of a certain specific absolute value of the vibration waveforms in a cumulative frequency distribution curve to a maximum value (Xp) of the vibration waveforms, and diagnosing the degree of fault in the machinery or equipment from the magnitude of the ratio (xcex21).
According to a second aspect of the present invention, a fault diagnosis method is provided, which comprises the steps of detecting vibration waveforms being generated by machinery or equipment, obtaining the ratio (xcex22) of a certain specific absolute value of the vibration waveforms to an effective value ("sgr") of the vibration waveforms, and diagnosing the degree of a fault of the machinery or equipment from the scale of the ratio (xcex22).
According to a third aspect of the present invention, a fault diagnosis method is provided, which comprises the steps of detecting vibration waveforms being generated by machinery or equipment, obtaining a root-mean-cubic value (xcex23) and a root-mean-quartic value (xcex24) which are statistics from data in which the vibration waveforms obtained are normalized at a certain specific absolute value of the vibration waveforms in a cumulative frequency distribution curve, and diagnosing the degree of fault in the machinery or equipment from the magnitude of the root-mean-cubic value (xcex23) and the root-mean-quartic value (xcex24).
According to a fourth aspect of the present invention, in any of the fault diagnosis methods above, the certain specific absolute value of the vibration waveforms in the cumulative frequency distribution curve is a value (an equivalent effective value: "sgr"eq) of 68.3% of the cumulative frequency.
According to a fifth aspect of the invention, a fault diagnosis apparatus is provided, which comprises vibration detecting means for detecting vibration waveforms being generated by machinery or equipment, cumulative frequency computing means for obtaining a cumulative frequency distribution curve of an absolute value of vibration waveforms detected by this vibration detecting means, maximum value detecting means for obtaining a maximum value (Xp) of the vibration waveforms detected by the vibration detecting means, peak ratio computing means for obtaining the peak ratio (xcex21) of a certain specific value in the cumulative frequency distribution curve computed by the cumulative frequency computing means to the maximum value (Xp) computed by the maximum value detecting means, and fault diagnosing means for diagnosing the degree of fault of the machinery or equipment from the scale of the peak ratio (xcex21) computed by this peak ratio computing means.
According to a sixth aspect of the present invention, a fault diagnosis apparatus is provided, which comprises vibration detecting means for detecting vibration waveforms being generated by machinery or equipment, cumulative frequency computing means for obtaining a cumulative frequency distribution curve of an absolute value of the vibration waveforms detected by this vibration detecting means, effective value computing means for obtaining an effective value ("sgr") of the vibration waveforms detected by the vibration detecting means, effective value ratio computing means for obtaining an effective value ratio (xcex22) of a certain specific value in the cumulative frequency distribution curve computed by the cumulative frequency computing means to the effective value ("sgr") computed by the effective value computing means, and fault diagnosing means for diagnosing the degree of fault of the machinery or equipment from the scale of the effective value ratio (xcex22) computed by this effective value ratio computing means.
According to a seventh aspect of the present invention, a fault diagnosis apparatus is provided, which comprises vibration detecting means for detecting vibration waveforms being generated by machinery or equipment, cumulative frequency computing means for obtaining a cumulative frequency distribution curve of an absolute value of the vibration waveforms detected by this vibration detecting means, normalizing means for normalizing the vibration waveforms obtained at a certain specific value in the cumulative frequency distribution curve computed by this cumulative frequency computing means, root-mean-cubic value and root-mean-quartic value computing means for obtaining a root-mean-cubic value (xcex23) and a root-mean-quartic value (xcex24) from data normalized by this normalizing means, fault diagnosing means for diagnosing the degree of fault of the machinery or equipment from a scale (size) of the root-mean-cubic value (xcex23) and the root-mean-quartic value (xcex24) computed by the root-mean-cubic value and root-mean-quartic value computing means.
According to a eighth aspect of the present invention, in any of the fault diagnosis apparatus above, the certain specific value of the absolute value of the vibration waveforms in the cumulative frequency distribution curve is a value (an equivalent effective value: "sgr"eq) of 68.3% of the cumulative frequency.